In the art of heating, ventilating and air conditioning (HVAC) equipment there has been a continuing desire and need for a system and method for controlling indoor air flowrate due to varying circumstances and the types of equipment used in HVAC systems. For example, in many residential HVAC systems, the occupants of the house or dwelling being air conditioned may have a desire to vary the air flowrate, hence speed, of the indoor blower or fan which circulates the conditioned air throughout the dwelling. In situations where the humidity being sensed by the dwelling occupants needs to be reduced by varying amounts, such can be accomplished by changing the air flowrate over the air cooling heat exchanger, such as a vapor compression system evaporator coil. In other circumstances, such as for systems which utilize heat pumps for both heating and cooling, the occupants of the dwelling may desire to reduce air flow in the heating mode in order to have a sense of warmer air being circulated during system operation.
Still further, the occupants of a dwelling or other facility being air conditioned by a forced air HVAC system, may desire to operate the indoor air circulation blower or fan continuously and at selected variable speeds to control air flowrate and noise level, for example. Of course, the occupants of a dwelling or building being air conditioned by a forced air HVAC system may also have the desire to control indoor blower or fan speed and air circulation rate during startup and shutdown phases of operation of the system so as to be able to capture residual heating or cooling effect after system shutoff and to minimize the loss of heated or cooled air due to heat transfer in the system ductwork during periods of system shutoff. Accordingly, it is to provide the capability of changing air flowrates in an HVAC system to satisfy several needs and desires, including those mentioned above, that the present invention has been developed.